Conventionally, as a synchronous machine mounted and used on a vehicle, various machines having a stator with a stator core to which a stator coil made of a plurality of phase windings for forming a rotating magnetic field is wound, and a rotor that rotates while facing a peripheral surface of the stator with an electromagnetic gap therebetween are known.
As a kind of the synchronous machine, a field winding type synchronous machine is disclosed in the Japanese Patent Application Laid-Open Publication No. 2008-178211.
The field winding type synchronous machine mentioned above has a rotor. The rotor has a rotor core having a plurality of main pole portions that cause a magnetic flux to flow to a stator core. The main pole portions are spaced apart by a predetermined electrical angle pitch from each other and project toward the stator. The rotor also has main pole windings wound around each of the main pole portions of the rotor core to produce the flux.
Although this field winding type synchronous machine is producing torque by interlinking an exciting magnetic flux directly with the main pole portions of the rotor core to excite the main pole windings, there is a problem that torque ripple becomes large.
In addition, other field winding type synchronous machines are disclosed also in Japanese Patent Application Laid-Open Publication Nos. 2010-22185, 2015-15846, and 2015-23767.
Each of these field winding type synchronous machines has interpole portions and interpole windings. The interpole portions project toward the stator and are spaced apart at roughly 90 degrees in electrical angle with respect to main pole portions of the rotor core. The interpole windings are wound around the interpole portions and produce an induced current by harmonic currents superimposed on a magnetic flux generated by the stator coil.
These field winding type synchronous machines produce torque by inducing an excitation current generated in the stator coil in the interpole windings disposed between the main pole portions, and supplying the induced current to the main pole windings.
In these cases, the torque ripples are small; however, since the induced current harmonic currents, caused by the interpole portions which are saturated at maximum load, are small, there is a problem that sufficient torque cannot be generated.